1. Field of the Invention
The present invention relates generally to an apparatus and method for managing sessions in a wireless communication system. In particular, the present invention relates to a method and system for managing sessions upon a change in a subnet of an access terminal (AT) in a mobile communication system, and an apparatus therefor.
2. Description of the Related Art
In general, wireless communication systems have been developed to make up for a defect of the fixed wire network that cannot be connected up to a terminal. The typical wireless communication systems include not only the general communication system supporting voice and data services, but also wireless Local Area Network (LAN), Wireless Broadband (Wibro), and Mobile Ad-Hoc network.
A mobile communication system enables a subscriber to make a call even while on the move at high speed over a wide area. The typical mobile communication system includes a cellular system. The cellular system, proposed to overcome the service area limitation and the subscriber capacity limitation of the conventional mobile communication system, divides the full service area into a plurality of small zones, or cells, and allows two cells fully spaced apart from each other to use the same frequency band, thereby spatially reusing the frequency. Advance Mobile Phone System (AMPS) and Total Access Communication Services (TACS), which are the earliest analog cellular technologies, are called first generation (1G) mobile communication. It is difficult to accommodate the rapidly increasing number of mobile communication service subscribers only with the 1G mobile communication system. Furthermore, with the development of the communication technology, there is an increasing demand not only for the conventional voice service but also for various data services. To meet the demands, second generation (2G) digital mobile communication was proposed, which was advanced from the 1G mobile communication system. The 2G digital mobile communication system, unlike the 1G analog mobile communication system, digitalizes analog voice signals before voice coding and then performs digital modulation/demodulation using the 800 MHz frequency band. A multiple access technology is classified into a Time Division Multiple Access (TDMA) technology and a Code Division Multiple Access (CDMA). The 2G mobile communication system provides voice service and low-speed data service. The 2G system is classified into the IS-95 (CDMA) and IS-54 (TDMA) systems, both of which are adopted as standards in the United States, and the Global System for Mobile communication (GSM) system which is adopted as a standard in Europe. In addition, the Personal Communication Services (PCS) system is classified as a 2.5th generation (2.5G) mobile communication system, and uses the 1.8˜2 GHz frequency band. The 2G mobile communication systems were aimed at increasing the efficiency of the mobile communication systems, while providing voice service to users. However, the advent of the Internet and users' demands for fast data service have created a need for a new wireless platform. The new wireless platform includes 3rd generation (3G) mobile communication such as International Mobile Telecommunication-2000 (IMT-2000).
A description will now be made of a 3G synchronous CDMA mobile communication system.
CDMA2000 1X service enables wireless Internet use at a rate of a maximum of 144 Kbps using the IS-95C network. This is much higher than the rate of 14.4 Kbps or 56 Kbps supported in the existing IS-95A/B networks, from which the IS-95C network evolved. Therefore, the use of the CDMA2000 1X service improves the quality of the existing voice and wireless application protocol (WAP) services and provides various multimedia services (audio on demand (AOD), video on demand (VOD), and the like). The IS-95A/B networks are names of base station networks. The IS-95B network can support a wireless data rate of a maximum of 64 Kbps, whereas the IS-95C network for CDMA2000 1X supports a data rate of a maximum of 144 Kbps. A CDMA2000 1X mobile phone, if any, may access an available IS-95A or IS-95B network, if no IS-95C network is installed in the corresponding area.
Despite development of the mobile communication technology, users still require even higher-quality data services. To meet these requirements, CDMA 2000 1x Evolution-Data Only (EV-DO) technology, also known as High Rate Packet Data (HRPD) technology, has been proposed. The CDMA 2000 1x EV-DO is a dedicated protocol for packet data transmission, which is fully different from the existing IS-2000 radio protocol, and supports a data rate of a maximum of 2.4 Mbps in the forward direction. The CDMA 2000 1x EV-DO requires a separate base station apparatus, different from that of the IS-2000, but shares the other system and network elements with the IS-2000.
Because the service received at the terminal from the system is superior to the service received at the system from the terminal due to the characteristics of packet data, CDMA 2000 1x EV-DO has a structure in which the forward channel speed is different from the reverse channel speed. When space diversity is not used for the terminal, CDMA 2000 1x EV-DO has an asymmetrical data rate structure in which a forward data rate is possible up to a maximum of 2.4 Mbps while a reverse data rate is possible up to a maximum of 153.6 Kbps.
IS-2000 has a limitation in the maximum data rate because it basically realizes high-speed packet data service based on a voice protocol. IS-2000 Release 0 can transmit packet data at up to 153.6 Kbps in a wireless section. But, the service provider can only support a data rate of up to 64 Kbps for Video-On-Demand (VOD) and a data rate of up to 32 Kbps on average for the wireless Internet because of the capacity problem in the wireless section. However, the CDMA 2000 1x EV-DO system basically aimed at packet data service cannot fully solve the capacity problem in the wireless section.
CDMA 2000 1x EV-DO, which is a protocol optimized only for the high-speed packet transmission, uses 1.25 MHz CDMA channels having the same frequency band as that of the current cdma2000 system. In particular, CDMA 2000 1x EV-DO dynamically assigns a data rate of each subscriber in the wireless section, and maximizes the efficiency of the wireless section and the system by making the best use of the unique characteristics of the packet data.
The CDMA 2000 1x EV-DO system is called an HRPD system, and in the CDMA 2000 1x EV-DO system, an access terminal (AT) uses a temporary identifier, called a Unicast Access Terminal Identifier (UATI). The AT is assigned a unique UATI from a Packet Control Function (PCF) in units of subnets, and performs a session negotiation process, an authentication process, a connection setup process, and a Point-to-Point Protocol (PPP) setup process, using the assigned UATI. When the AT in a dormant state moves to a new subnet, it is assigned a new UATI and acquires session information from the old subnet.
In this specification, the old subnet in which the AT was located before its movement will be referred to as a “source subnet” and the new subnet to which the AT has moved will be referred to as a “target subnet.” A definition of the terms “source” and “target” can be also be used for an access network (AN) and the PCF, also known as a packet controller.
In the general CDMA 2000 1x EV-DO (HRPD), when an AT moves from a source subnet to a target subnet with the radio link lost or with its power off, and newly accesses the target subnet, because an AN of the target subnet has no session information for the corresponding AT, the AT must perform a new session negotiation process with the target AN and perform again the connection setup process.
In addition, when session information for the AT is continuously stored in a source PCF, the session information is deleted only by an inner timer. This routine is inefficient because the session information is unnecessarily stored until the timeout expires, taking an operation range of the timer into account.
Accordingly, there is a need for an improved method and system for managing session information.